CN110248979B

CN110248979B - Aqueous coating composition

Info

Publication number: CN110248979B
Application number: CN201880010368.2A
Authority: CN
Inventors: 艾瑟·范卡斯特恩; 罗纳德·坦尼布罗克; 格拉达斯·可纳利斯·奥佛比克; 焦拉林·塞莱斯汀
Original assignee: Kostron Netherlands Co ltd
Current assignee: Covestro Netherlands BV
Priority date: 2017-02-08
Filing date: 2018-02-07
Publication date: 2022-07-22
Anticipated expiration: 2038-02-07
Also published as: CN110248977A; US11384252B2; US11274229B2; EP3960784A1; EP3580249B1; EP3580250A1; EP3580249A1; US20200095460A1; EP3580256B1; EP3580256A1; DK3580256T3; WO2018146145A1; US20200024474A1; EP3580255B1; CN110352204B; CN110352204A; ES2905925T3; EP3580255A1; CN110248979A; US11124671B2

Abstract

The invention relates to an aqueous coating composition comprising a polyurethane a and a vinyl polymer, wherein the polyurethane a comprises as structural units at least the following: (a) a polyisocyanate containing at least two cyclic groups, (b) a non-cyclic aliphatic diisocyanate in which the non-cyclic aliphatic group linking the two isocyanate groups has 4 to 36 carbon atoms, and (c) a component containing isocyanate-reactive groups, wherein the total amount of (a) and (b) is 10 to 60% by weight, relative to the total weight of the components used to prepare polyurethane a; and wherein the weight ratio between (a) and (b) is in the range of 50:50 to 99: 1.

Description

Aqueous coating composition

The present invention relates to aqueous coating compositions comprising polyurethane and vinyl polymer, to a process for preparing such compositions and to substrates having coatings derived from such compositions.

It is well known in the coatings industry that polyurethane adhesives can be applied to a variety of substrates to provide coatings with good mechanical and chemical resistance.

Urethane adhesives typically require solvents during the manufacturing process in order to reduce the viscosity of the prepolymer to acceptable values. However, regulations regarding the presence of VOCs (volatile organic components) in adhesives for indoor applications are under pressure. Therefore, the use of VOC-containing solvents in the preparation of urethane prepolymers is becoming less preferred, and the removal of these solvents after preparation requires a lot of effort and energy. The use of vinyl monomers as diluents has shown A good alternative to VOC containing solvents, as described in WO-A-2005/058995, resulting in urethane acrylic hybrids. The polyurethanes are obtained from a polyurethane prepolymer (a) obtained by reacting a polyisocyanate, in particular H, and an isocyanate-reactive compound, with an active hydrogen chain extending compound (b)₁₂MDI (i.e., dicyclohexylmethane-4, 4' -diisocyanate, having typically less than 10% by weight of isomers of dicyclohexylmethane-4, 4' -diisocyanate (especially dicyclohexylmethane-2, 4' -diisocyanate)).

It has been found that urethane-vinyl containing waterborne coating compositions as described in WO-A-2005/058995 result in A high minimum film formation temperature MFFT. It is well known that the MFFT of a coating composition can be reduced by the presence of a coalescent agent. However, regulations regarding the presence of coalescents are becoming increasingly stringent, as coalescents may, for example, cause skin irritation and have a negative impact on (indoor) air quality, and/or increasing the amount of coalescents may increase the amount of Volatile Organic Compounds (VOCs) in the coating composition.

It is an object of the present invention to reduce the amount of coalescent agent required to obtain a particular MFFT in an aqueous coating composition comprising polyurethane and vinyl polymer, while the contamination resistance of the coating to ammonia, water, ethanol, coffee and/or red wine is maintained at least at a sufficient level.

The object of the present invention is achieved by providing an aqueous coating composition comprising a polyurethane a and a vinyl polymer, wherein the polyurethane a is obtained by reaction of at least the following components:

(a) a polyisocyanate containing at least two cyclic groups,

(b) a non-cyclic aliphatic diisocyanate in which the non-cyclic aliphatic group linking the two isocyanate groups has 4 to 36 carbon atoms, and

(c) a component containing isocyanate-reactive groups, wherein,

wherein the total amount of (a) and (b) is 10-60% by weight relative to the total weight of the components used to prepare polyurethane A; and is provided with

Wherein the weight ratio between (a) and (b) is in the range of 50:50 to 99: 1.

It has surprisingly been found that the MFFT of the coating composition can be reduced by using the claimed polyurethane a compared to the use of a polyurethane based on polyisocyanate (a) but without diisocyanate (b), thus obtaining a weight ratio between (a) and (b) of 100:0, and furthermore that the contamination resistance against ammonia, water, ethanol, coffee and/or red wine is at least maintained at a sufficient level.

Methods of preparing polyurethanes are known in the art and are described, for example, in Polyurethane Handbook, 2 nd edition, published by Carl Hanser, G.Oertel, 1994. The polyurethanes A present in the aqueous coating compositions can be prepared in a conventional manner by at least (a), (b) and (c) according to methods well known in the art. Generally, the isocyanate-terminated polyurethane prepolymer (I) is first formed by reaction of components (a), (b) and (c) and then preferably chain-extended with an active hydrogen-containing compound (II).

Component (a)

Component (a) is a polyisocyanate containing at least two cyclic groups. "cyclic" is defined herein as a closed ring of carbon atoms, either aromatic or aliphatic. Preferably, component (a) is a diisocyanate. Component (a) is preferably a polyisocyanate containing at least two cycloaliphatic groups, a polyisocyanate containing at least two aromatic groups, a polyisocyanate containing at least one cycloaliphatic group and at least one aromatic group, and any mixtures thereof. More preferably, component (a) is a polyisocyanate containing at least two cycloaliphatic groups.

The polyisocyanate containing at least two aromatic groups is preferably a polyisocyanate containing at least two aromatic C6 groups, even more preferably containing two aromatic C6 groups. Non-limiting examples of component (a) containing at least two aromatic groups are methylene bis (phenyl isocyanate) (all isomers) and 3,3 '-dimethyl-4, 4' -biphenyl diisocyanate (CAS number 91-97-4). More preferably, the polyisocyanate containing at least two aromatic groups is methylene bis (phenyl isocyanate) (all isomers). Even more preferably, the polyisocyanate containing at least two aromatic groups is a mixture of 4,4 '-methylenebis (phenyl isocyanate) and 2,4' -methylenebis (phenyl isocyanate).

More preferably, component (a) is a polyisocyanate containing at least two cycloaliphatic groups, even more preferably two cycloaliphatic groups. Even more preferably, component (a) is a polyisocyanate containing at least two cyclohexane groups, even more preferably two cyclohexane groups. A preferred example of a polyisocyanate containing at least two cyclohexane groups is dicyclohexylmethane diisocyanate (all isomers). Even more preferably, component (a) is H12MDI (CAS number 5124-30-1).

Component (b)

Component (b) is a non-cyclic aliphatic diisocyanate in which the non-cyclic aliphatic group linking the two isocyanate groups contains from 4 to 36 carbon atoms. Non-cyclic aliphatic diisocyanates are those which comprise only linear or branched aliphatic chains. As used herein, a non-cyclic aliphatic Cx-Cy diisocyanate refers to a diisocyanate in which two isocyanate groups are connected by a non-cyclic aliphatic group containing x to y carbon atoms.

Preferably, component (b) is an acyclic aliphatic C4-C18 diisocyanate, more preferably an acyclic aliphatic C4-C12 diisocyanate, more preferably an acyclic aliphatic C4-C9 diisocyanate, even more preferably an acyclic aliphatic C4-C8 diisocyanate, even more preferably an acyclic aliphatic C4-C6 diisocyanate. Non-limiting examples of component (b) are 1, 4-butane diisocyanate (CAS number 4538-37-8), 1, 6-hexane diisocyanate (CAS number 822-06-0), 1, 8-octane diisocyanate (CAS number 10124-86-4), mixtures of 2,2, 4-trimethyl-hexamethylene diisocyanate and 2,4, 4-trimethyl-hexamethylene diisocyanate (CAS number 32052-51-0). Most preferably, component (b) is 1, 6-diisocyanatohexane (also known as 1, 6-hexane diisocyanate) (CAS number 822-06-0).

The total amount of (a) and (b) is from 10 to 60% by weight, more preferably from 20 to 55% by weight, even more preferably from 25 to 50% by weight, relative to the total weight of the components used to prepare polyurethane a. To reduce costs and provide a range of coating properties, the polyisocyanates (a) and (b) may be combined with one or more different polyisocyanates selected from the more conventional types used in coating compositions. The polyisocyanates (a) and (b) preferably represent at least 70% by weight, preferably at least 90% by weight and most preferably 100% by weight of the total weight of the polyisocyanates used for preparing the polyurethane a.

(a) The weight ratio of (a) to (b) is from 50:50 to 99:1, preferably from 60:40 to 95:5, more preferably from 65:35 to 90:10, even more preferably from 70:30 to 90: 10.

Component (c)

Component (c) is a component containing at least one isocyanate-reactive group, also referred to as isocyanate-reactive component (c). Preferred isocyanate-reactive groups are hydroxyl groups.

Component (c) preferably comprises an isocyanate-reactive component containing ionic and/or potentially ionic water-dispersing groups (component (c) (i)). Containing ions or latent ions relative to the total weight of the components used to prepare polyurethane AThe amount of isocyanate-reactive component of the ionic water-dispersing groups is generally from 1 to 15% by weight, preferably from 3 to 12% by weight, even more preferably from 4 to 10% by weight. As used herein, a latent anionic dispersing group refers to a group that can be converted to an anionic group by salt formation (i.e., deprotonation of the group by a base) under polyurethane preparation reaction conditions. Preferred ionic water-dispersing groups are anionic water-dispersing groups. Preferred anionic water-dispersing groups are carboxylic, phosphoric and/or sulphonic acid groups. Examples of these components (c) include carboxyl group-containing diols, for example dihydroxyalkanoic acids such as 2, 2-dimethylolpropionic acid (DMPA) or 2, 2-dimethylolbutanoic acid (DMBA). Alternatively, sulfonic acid groups may be used as the latent anionic water-dispersing groups. The anionic water-dispersing groups are preferably in the form of salts, wholly or in part. The conversion into salt form is optionally carried out by neutralizing the polyurethane prepolymer with a base, preferably during the preparation of the polyurethane prepolymer and/or during the preparation of the aqueous composition of the invention. If the anionic water-dispersing groups are neutralized, the base used to neutralize the groups is preferably ammonia, an amine or an inorganic base. Suitable amines include tertiary amines such as triethylamine or N, N-dimethylethanolamine. Suitable inorganic bases include alkali metal hydroxides and carbonates, for example lithium hydroxide, sodium hydroxide or potassium hydroxide. Quaternary ammonium hydroxides, e.g. N, may also be used⁺(CH₃)₄(OH). Bases are typically used as neutralizing agents, which produce counterions that may be required for the composition. For example, preferred counterions include Li⁺、Na⁺、K⁺、NH₄ ⁺And substituted ammonium salts. Cationic water-dispersible groups may also be used, but are less preferred. Examples include pyridyl, imidazolyl and/or quaternary ammonium groups, which can be neutralized or permanently ionized (e.g., with dimethyl sulfate). A very suitable isocyanate-reactive component containing ionic or potentially ionic water-dispersing groups is dimethylolpropionic acid (DMPA). The amount of neutralizing agent used is preferably such that the molar ratio of ionic and potentially ionic water-dispersing groups to neutralizing groups of the neutralizing agent is in the range of from 0.3 to 1.5, more preferably from 0.5 to 1.2, even more preferably from 0.6 to 0.98. In preferred aqueous coating compositions of the invention, the neutralizing agent is a metal salt and/or ammonia.

Component (c) may also include an isocyanate-reactive component containing nonionic water-dispersing groups (further referred to as component (c) (ii)). Preferred nonionic water-dispersing groups are polyalkylene oxide groups, more preferably polyethylene oxide groups. A small portion of the polyethylene oxide groups may be replaced by propylene oxide segments and/or butylene oxide segments, but the polyethylene oxide groups should still contain ethylene oxide as a major component. Preferred ethylene oxide chain lengths are >4 ethylene oxide units, preferably >8 ethylene oxide units, most preferably >15 ethylene oxide units. Preferably, the Mw of the polyethyleneoxy group is from 175 to 5000 daltons, more preferably from 350 to 2200 daltons, most preferably from 660 to 2200 daltons. The amount of the isocyanate-reactive component containing nonionic water-dispersing groups (component (c) (ii)) is generally from 0 to 15% by weight, preferably from 0 to 10% by weight, even more preferably from 1 to 5% by weight, relative to the total weight of the components used to prepare polyurethane a.

Component (c) typically also comprises at least one isocyanate-reactive component (c) (iii) different from component (c) (i) and component (c) (ii). The isocyanate-reactive component (c) (iii) may be selected from any chemical class of mono-and/or polyols useful in polyurethane synthesis and is different from any other component (c). The number average molecular weight of the component (c) (iii) is preferably 500-6000. As used herein, the number average molecular weight of the hydroxyl-containing component is determined by multiplying the equivalent weight of the component by the OH functionality of the component (the OH functionality of the polyol is given by the supplier; if the polyol is a diol, the OH functionality is 2). The equivalent weight of the component is calculated by dividing 56100 by the OH number of the component. The OH number of the components was measured by titration of a known mass of the component according to ASTM D4274, expressed as mg KOH/g.

In particular, the isocyanate-reactive component (c) (iii) may be a polyester polyol, a polyesteramide polyol, a polyether polyol, a polythioether polyol, a polycarbonate polyol, a polyacetal polyol, a polyvinyl polyol and/or a polysiloxane polyol. Preferably, the isocyanate-reactive component (c) (iii) is selected from polyester (amide) polyols, polyether polyols, polycarbonate polyols and any mixtures thereof. The amount of component (c) (iii) is generally at least 60 wt%, preferably at least 70 wt%, most preferably at least 85 wt%, relative to the total weight of component (c).

The amount of component (c) is preferably from 40 to 90% by weight, more preferably from 45 to 80% by weight, even more preferably from 50 to 75% by weight, relative to the total weight of the components used to prepare polyurethane a.

The acid value of the polyurethane A in the aqueous coating composition is preferably from 5 to 65mg KOH/g polyurethane A. As used herein, the acid number of polyurethane A is determined according to DTN-EN ISO 2114.

Vinyl polymers

In addition to the polyurethane, the coating composition of the present invention also comprises a vinyl polymer, in particular an acrylic polymer. The presence of the polyurethane and vinyl polymer may be carried out by means of a simple blend of preformed polyurethane and vinyl polymer dispersions or preferably by in situ polymerisation of vinyl monomers in the presence of preformed polyurethane to form a hybrid system. Polyurethane vinyl polymer hybrids refer to the preparation of vinyl polymers by free radical polymerization of vinyl monomers in the presence of polyurethane.

Preferably, the weight ratio of polyurethane to vinyl polymer present in the polyurethane vinyl polymer hybrid is from 95:5 to 15:85, more preferably from 90:10 to 20:80, most preferably from 80:20 to 30: 70.

The vinyl polymers are obtained by polymerizing vinyl monomers using conventional free radical generating initiator systems. Suitable free radical generating initiators include mixtures that partition between an aqueous phase and an organic phase. Suitable free radical generating initiators include inorganic peroxides such as ammonium persulfate hydrogen peroxide, hydrogen peroxide; organic peroxides, such as benzoyl peroxide; alkyl hydroperoxides such as tert-butyl hydroperoxide and cumene hydroperoxide; dialkyl peroxides, such as di-tert-butyl peroxide; peroxy esters such as t-butyl perbenzoate and the like; mixtures may also be used. In some cases, the peroxy compound is advantageously used in combination with a suitable reducing agent, such as erythorbic acid (redox system). Azo compounds such as azobisisobutyronitrile may also be used. EDTA (EDTA is ethylenediaminetetraacetic acid) can also be effectively used as part of the redox initiator system. The amount of initiator or initiator system used is conventional, for example in the range of from 0.05 to 6% by weight, based on the weight of the vinyl monomers used.

Preferably, at least 80 wt%, more preferably at least 95 wt%, most preferably 100 wt% of the total weight of vinyl monomers used is alpha, beta-monounsaturated vinyl monomer.

Examples of vinyl monomers include, but are not limited to, 1, 3-butadiene, isoprene; trifluoroethyl (meth) acrylate (TFEMA); dimethylaminoethyl (meth) acrylate (DMAEMA); styrene, α -methylstyrene, (meth) acrylamide and (meth) acrylonitrile; vinyl halides such as vinyl chloride; vinylidene halides, such as vinylidene chloride; a vinyl ether; vinyl esters, such as vinyl acetate, vinyl propionate, vinyl laurate; vinyl esters of pivalic acid, such as VeoVa 9 and VeoVa 10(VeoVa is a trademark of Resolution); a heterocyclic vinyl compound; alkyl esters of monoethylenically unsaturated dicarboxylic acids, e.g. di-n-butyl maleate and di-n-butyl fumarate, especially of formula CH₂＝CR⁴-COOR⁵Of acrylic and methacrylic acid, wherein R⁴Is H or methyl and R⁵Is an optionally substituted alkyl or cycloalkyl group of 1 to 20 carbon atoms, more preferably 1 to 8 carbon atoms, examples of which are methyl methacrylate, ethyl methacrylate, n-butyl (meth) acrylate (all isomers), octyl (meth) acrylate (all isomers), 2-ethylhexyl (meth) acrylate, isopropyl (meth) acrylate and n-propyl (meth) acrylate. Preferred formula CH₂＝CR⁴-COOR⁵The monomers of (b) include butyl (meth) acrylate (all isomers), methyl (meth) acrylate, octyl (meth) acrylate (all isomers) and ethyl (meth) acrylate. Preferably, at least 30 wt%, more preferably at least 50 wt%, even more preferably at least 70 wt% of the total amount of vinyl monomers used to prepare the vinyl polymer is selected from the group consisting of: methyl methacrylate, butyl acrylate, butyl methacrylate, propyleneNitriles, styrene and mixtures of two or more of said monomers. Preferably, the vinyl monomer used to prepare the vinyl polymer is selected from the group consisting of styrene, methyl methacrylate, butyl acrylate, butyl methacrylate, and mixtures thereof. More preferably, at least 30 wt%, preferably at least 50 wt%, more preferably at least 70 wt% of the total amount of vinyl monomers used to prepare the vinyl polymer is selected from styrene or methyl methacrylate.

The vinyl monomer may include a vinyl monomer having a functional group, for example, a crosslinker group and/or a water-dispersing group. Such functional groups may be introduced directly into the vinyl polymer by free radical polymerization, or the functional groups may be introduced by reaction of a reactive vinyl monomer, which is subsequently reacted with a reactive compound bearing the desired functional group. Examples of suitable vinyl monomers providing crosslinking groups include acrylic and methacrylic monomers having at least one free carboxyl or hydroxyl group, epoxy group, acetoacetoxy group or carbonyl group, such as acrylic and methacrylic acid, glycidyl acrylate, glycidyl methacrylate, acetoacetoxyethyl methacrylate, allyl methacrylate, tetraethylene glycol dimethacrylate, divinylbenzene and diacetone acrylamide.

Vinyl monomers that provide ionic or potentially ionic water-dispersing groups that can be used as additional vinyl monomers include, but are not limited to, (meth) acrylic acid, itaconic acid, maleic acid, citraconic acid, and styrene sulfonic acid. Preferably, the level of vinyl monomer providing ionic or potentially ionic water-dispersing groups is from 0 to 5 wt%, more preferably from 0 to 1 wt%, most preferably less than 0.5 wt% of the total level of vinyl monomer used.

Vinyl monomers providing the nonionic water-dispersing groups include alkoxy polyethylene glycol (meth) acrylates, which preferably have a number average molecular weight of 140-3000. Examples of commercially available monomers of this type include omega-methoxypolyethylene glycol (meth) acrylate.

Preferably, the weight average molecular weight (Mw) of the resulting vinyl polymer is at least 60000 daltons, more preferably 100000-.

Coalescing agents (also known as coalescents or coalescents) are used in coating compositions (e.g., paints) to optimize the film-forming process of the polymeric binder particles. The film-forming process in the coating composition involves coalescence of the polymer particles during and after evaporation of the diluent (which in the present invention is primarily water), allowing contact and fusing of adjacent polymer dispersion particles. Coalescing agents generally lower the minimum film-forming temperature of the coating composition. A non-limiting example of a coalescing agent is an organic co-solvent. Organic co-solvents may be added before, during or after polyurethane formation to control viscosity. Examples of co-solvents that also have coalescing functionality include water miscible solvents such as 1-methyl-2-pyrrolidone, glycol and glycol ethers (e.g., butyl diglycol, dipropylene glycol methyl ether), acetone, methyl ethyl ketone and alkyl ethers of ethylene glycol acetate, or mixtures thereof.

It has been surprisingly found that with the compositions of the present invention, the minimum film forming temperature can be reduced without having to increase the amount of coalescent in the coating composition. It has surprisingly been found that the coating composition of the present invention can have a minimum film forming temperature of less than 50 ℃, even less than 35 ℃, even less than 25 ℃, even less than 20 ℃, even less than 5 ℃, even when the coating composition contains a reduced amount of coalescent agent. As used herein, reduced amount of coalescent means that the coating composition contains less than 10% by weight coalescent, preferably less than 5% by weight coalescent, more preferably less than 3% by weight coalescent, more preferably less than 1% by weight coalescent, based on the solids content of the coating composition of the present invention by weight. By the composition of the invention, minimum film forming temperatures below 50 ℃, even below 35 ℃, even below 25 ℃, even below 20 ℃ can be obtained even in the absence of coalescents in the aqueous coating composition. The solids content is determined by evaporating volatile compounds, such as water and optionally solvents and volatile amines, present in the aqueous coating composition.

Furthermore, small amounts of organic co-solvents are advantageous in view of the level of volatile organic co-solvents (VOC) and possible flammability risks. Especially with respect to 1-methyl-2-pyrrolidone (NMP), regulations regarding labeling of products containing NMP are becoming more and more stringent. Therefore, a minimum amount of or absence of NMP is required. The amount of 1-methyl-2-pyrrolidone in the aqueous coating composition is preferably less than 3 wt%, preferably less than 1 wt%, more preferably less than 0.5 wt%, and even more preferably 0 wt% of the solids content of the coating composition. Furthermore, since the presence of free vinyl monomers in the coating composition or in the coating obtained from the coating composition may cause skin irritation, low residual amounts or even no residual amounts of free (non-polymeric) vinyl monomers are required.

The aqueous coating composition of the present invention preferably comprises tin in an amount of at most 50ppm, more preferably at most 10ppm, even more preferably at most 5ppm, even more preferably at most 2ppm, even more preferably the aqueous coating composition of the present invention is tin-free. The aqueous coating composition of the invention preferably contains a tertiary amine, such as triethylamine, preferably in an amount of at most 1.5 wt.% (relative to the aqueous coating composition), more preferably at most 1 wt.%, even more preferably at most 0.5 wt.%, even more preferably at most 0.1 wt.%, even more preferably the aqueous coating composition of the invention is free of tertiary amine.

The aqueous coating composition according to the present invention may further comprise other polymer binders in addition to the polyurethane a and the vinyl polymer. The total amount of polyurethane a and vinyl polymer present in the aqueous coating composition is preferably from 20 to 55% by weight, preferably from 25 to 50% by weight (relative to the total weight of the aqueous coating composition).

The present invention further relates to a process for preparing an aqueous coating composition as described above, comprising the steps of:

I. preparing an isocyanate-terminated polyurethane prepolymer by reacting at least components (a), (b) and (c):

(a) a polyisocyanate containing at least two cyclic groups,

(c) a component containing at least one isocyanate reactive group, said component (c) comprising:

(c) (i) an isocyanate-reactive component containing ionic and/or potentially ionic water-dispersing groups, and/or

(c) (ii) an isocyanate-reactive component containing nonionic water-dispersing groups, and/or

(c) (iii) isocyanate-reactive components other than those comprised by (c) (i) and (c) (ii);

(d) adding 0-40 wt% of diluent in the step I,

wherein the total amount of (a) and (b) is 10-60% by weight relative to the total weight of the components used to prepare polyurethane A; and the weight ratio between (a) and (b) is from 50:50 to 99: 1; and the amount of (d) is given with respect to (a), (b), (c) and (d);

either mixing the isocyanate-terminated polyurethane prepolymer with an aqueous phase comprising a neutralizing agent and optionally further chain extending compounds or neutralizing the isocyanate-terminated polyurethane prepolymer by adding the neutralizing agent to the isocyanate-terminated polyurethane prepolymer and subsequently (i) adding the neutralized isocyanate-terminated polyurethane prepolymer to water optionally comprising further chain extending compounds or (ii) adding water optionally comprising further chain extending compounds to said neutralized isocyanate-terminated polyurethane prepolymer; and

wherein at the start of the reaction to produce the isocyanate-terminated polyurethane prepolymer, the process comprises either reacting (a): at least one of components (c) (i), (c) (ii) and (c) (iii) and components (a) and (B), or (B): at least two of components (b), (C) (i), (C) (ii) and (C) (iii) and component (a), or (C): feeding at least two of components (a), (c) (i), (c) (ii) and (c) (iii) and component (b) to a reactor; and

wherein the preparation of polyurethane a is carried out in the presence of less than 3 wt% of 1-methyl-2-pyrrolidone, preferably less than 1 wt% of 1-methyl-2-pyrrolidone, more preferably less than 0.5 wt% of 1-methyl-2-pyrrolidone, based on the weight of polyurethane a, most preferably the preparation of polyurethane a is carried out in the absence of 1-methyl-2-pyrrolidone; and

wherein (i) the vinyl polymer is introduced into the coating composition before, during or after the preparation of the polyurethane and/or (ii) a vinyl monomer is added before, during or after the preparation of the polyurethane and the vinyl monomer is prepared by: a free radical initiator is added in the presence of the polyurethane to polymerize the vinyl monomer.

In the process of the present invention, preference is given to using component (c) (i) for preparing polyurethane A. Component (c) (iii) is also preferably used for the preparation of polyurethane A.

The process comprises, at the start of the reaction for preparing the isocyanate-terminated polyurethane prepolymer, either reacting (a): at least one of components (c) (i), (c) (ii) and (c) (iii) and components (a) and (B), or (B): at least two of components (b), (C) (i), (C) (ii) and (C) (iii) and component (a), or (C): at least two of components (a), (c) (i), (c) (ii) and (c) (iii), and component (b), are fed to the reactor. At least a portion of the amount of these components is added to the reactor at the beginning of the reaction, or the entire amount of these components is added to the reactor at the beginning of the reaction. The preparation of the isocyanate-terminated polyurethane prepolymers is generally carried out at temperatures of from 30 to 130 c, preferably from 70 to 110 c. Preferably, the process comprises feeding at least one of components (c) (i), (c) (ii) and (c) (iii) and components (a) and (b) to a reactor at the start of the reaction to produce the isocyanate-terminated polyurethane prepolymer. More preferably, the process comprises feeding components (a), (b), (c) (i), (c) (iii) and optionally (c) (ii) to a reactor at the start of the reaction to produce an isocyanate-terminated polyurethane prepolymer.

Step I of the process of the present invention is preferably facilitated by the addition of 1 to 40 wt% of a diluent (relative to the total weight of the components used to prepare the isocyanate-terminated polyurethane prepolymer) to reduce the viscosity of the prepolymer, more preferably 5 to 35 wt% and even more preferably 10 to 25 wt% of a diluent is added. The diluent is preferably added at the beginning of the reaction of step I. In case the coating composition comprises a polyurethane-vinyl polymer hybrid, the diluent in step I is preferably a vinyl monomer. In addition, the diluent in step I is preferably an aprotic organic co-solvent. Examples of co-solvents include water miscible solvents such as acetone, methyl ethyl ketone, and alkyl ethers of ethylene glycol or propylene glycol and analogs thereof or alkyl ethers of ethylene glycol acetates and analogs thereof or mixtures thereof. The preferred diluent (d) (excluding vinyl monomers) is acetone because it can be easily removed from the coating composition at the end of the polyurethane preparation.

US-A-6147155 relates to A process for preparing aqueous polyurethane dispersions based on cyclic and acyclic diisocyanates, in particular H12MDI and Hexamethylene Diisocyanate (HDI) or isophorone diisocyanate (IPDI) and HDI being used as polyisocyanates. US-A-6147155 teaches that A multi-step process is required to prepare aqueous polyurethane dispersions with good processability, i.e. A cyclic diisocyanate is reacted in A first stage with A compound containing one or more isocyanate-reactive groups and at least one carboxylic acid or carboxylate group to form an intermediate product; after the preparation of this intermediate product, the remaining components, in particular the acyclic diisocyanates, are reacted with the intermediate product to form an NCO prepolymer. It was further found that the use of the coalescing agent 1-methyl-2-pyrrolidone (NMP) in the first stage is necessary to reduce the viscosity and to avoid phase separation and settling in the first stage. However, regulations on product labels containing NMP are becoming more stringent. Therefore, proposed modifications of the legislation on the labeling of products containing NMP have led to increased efforts to minimize or even eliminate the use of NMP. Therefore, the presence of a minimum amount of NMP or the absence of NMP is highly desirable. Furthermore, U.S. Pat. No. 3, 6147155 does not teach that the MFFT of waterborne polyurethane coating compositions can be reduced by using A polyisocyanate containing at least two cyclic groups and A non-cyclic aliphatic C4-C36 diisocyanate. The presence of a large amount of coalescent NMP in all examples resulted in a low MFFT (<5 ℃). Furthermore, it has been found that the use of a polyisocyanate containing at least two cyclic groups in combination with a non-cyclic aliphatic C4-C36 diisocyanate results in mechanical properties (such as hardness and blocking) and stain resistance that are not significantly affected, and possibly even better, than the use of a polyisocyanate containing one cyclic group (such as isophorone diisocyanate IPDI) and a non-cyclic aliphatic C4-C36 diisocyanate, while the increase in MFFT (due to the use of a polyisocyanate containing at least two cyclic groups) is surprisingly reduced, thus surprisingly reducing the coalescent requirements.

It has surprisingly been found that, contrary to the process described in US-A-6147155, component (A) and component (b) can be added at the start of the reaction for preparing the isocyanate-terminated polyurethane prepolymer if the preparation of polyurethane A and thus the preparation of the isocyanate-terminated polyurethane prepolymer is carried out in the presence of < 3% by weight of 1-methyl-2-pyrrolidone, preferably in the presence of less than 1% by weight of 1-methyl-2-pyrrolidone, more preferably in the presence of less than 0.5% by weight of 1-methyl-2-pyrrolidone, most preferably in the absence of 1-methyl-2-pyrrolidone. Thus, in the process of the present invention, the isocyanate-terminated polyurethane prepolymer can be prepared in a one-shot process. Furthermore, it has surprisingly been found that, contrary to the process described in US-A-6147155, well known chain extending compounds containing at least two primary amino groups, such as hydrazine and ethylenediamine, are suitable for chain extending the isocyanate-terminated polyurethane prepolymer in the process of the present invention. In the process described in US-A-6147155, it is necessary to use A chain extender which does not contain more than one uncapped primary or secondary amino group to overcome the difficulty of the chain extender reacting rapidly with any unreacted acyclic diisocyanate monomer present in the isocyanate-terminated polyurethane prepolymer. In the process of the present invention, it is not necessary to use chain extenders which do not contain more than one uncapped primary or secondary amino group, although they may also be used as chain extenders. Further, in view of the reduction in VOC content of the coating composition, it is preferable to use a compound containing an unblocked primary amino group and/or an unblocked secondary amino group.

In the present invention, the NCO of the isocyanate terminated polyurethane prepolymer: the OH molar ratio is preferably higher than 1, more preferably from 1.1 to 3, even more preferably from 1.3 to 2.2.

Preferably, the coating composition of the present invention comprises a polyurethane vinyl polymer hybrid. In this case, the process for preparing the aqueous coating composition according to the present invention preferably comprises the steps of:

(a) a polyisocyanate containing at least two cyclic groups,

(d) in step I0-35 wt% of vinyl monomer is added,

wherein the total amount of (a) and (b) is 10-60% by weight relative to the total weight of the components used to prepare polyurethane A; and is

(a) And (b) in a weight ratio of 50:50 to 99: 1; and is provided with

(d) The amounts of (a), (b), (c) and (d);

preferably, vinyl monomers are added; and

adding a free radical initiator to polymerize the vinyl monomer,

wherein, at the start of the reaction for preparing the isocyanate terminated polyurethane prepolymer, the process comprises either reacting (a): at least one of components (c) (i), (c) (ii) and (c) (iii) and components (a) and (B), or (B): at least two of components (b), (C) (i), (C) (ii) and (C) (iii) and component (a), or (C): feeding at least two of components (a), (c) (i), (c) (ii) and (c) (iii) and component (b) to a reactor; and is provided with

Wherein the preparation of polyurethane a is carried out in the presence of <3 wt% of 1-methyl-2-pyrrolidone, preferably in the presence of less than 1 wt% of 1-methyl-2-pyrrolidone, more preferably in the presence of less than 0.5 wt% of 1-methyl-2-pyrrolidone, most preferably in the absence of 1-methyl-2-pyrrolidone, based on the weight of polyurethane a; and is

Adding a vinyl monomer in step I and/or step III; and is provided with

The vinyl monomer is polymerized by adding a radical initiator in the presence of the polyurethane to polymerize the vinyl monomer.

Some or all of the vinyl monomer may be present at the beginning of the isocyanate-terminated prepolymer preparation, or some or all of the vinyl monomer may be added during the preparation, or some or all of the vinyl monomer may be added after the isocyanate-terminated prepolymer is prepared, or some or all of the vinyl monomer may be added to the aqueous phase in which the urethane prepolymer is dispersed, or some or all of the vinyl monomer may be added to the aqueous dispersion of the chain-extended polyurethane (thus after step II), in which case the vinyl monomer swells into the chain-extended polyurethane particles. The vinyl monomer is not polymerized until chain extension has been performed; thus, step IV is preferably performed after step I and step II, and in case step III is not optional, step IV is performed before step III, together with step III and/or after step III.

In a preferred embodiment of the process of the present invention, the neutralization and chain extension of the isocyanate-terminated polyurethane prepolymer is carried out by: neutralizing the isocyanate terminated polyurethane prepolymer, subsequently dispersing the neutralized isocyanate terminated polyurethane prepolymer in water to obtain a dispersion and then adding a chain extending compound, preferably a water diluted chain extending compound, to the dispersion.

Preferably, the isocyanate-terminated polyurethane prepolymer is chain extended with an active hydrogen-containing chain extension compound other than water. Active hydrogen-containing chain extending compounds that can be reacted with the isocyanate-terminated prepolymer include amino alcohols, primary or secondary diamines or polyamines (including compounds containing primary and secondary amino groups), hydrazine and substituted hydrazines. Examples of such chain extending compounds useful in the present invention include 2- (methylamino) ethylamine, aminoethylethanolamine, aminoethylpiperazine, diethylenetriamine, and alkylene diamines such as ethylenediamine, and cyclic amines such as isophorone diamine. Also, compounds such as hydrazine, azines such as acetone azine, substituted hydrazines such as dimethylhydrazine, 1, 6-hexamethylene dihydrazine, carbodihydrazines (carbodihydrazines), dicarboxylic acid hydrazides such as adipic acid dihydrazide, oxalic acid dihydrazide, isophthalic acid dihydrazide, sulfamates, hydrazides prepared by reacting a lactone with hydrazine, bis-semicarbazide (bis-semi-carbazide), and bis-hydrazide carbonates of diols are all useful. Preferred chain extending compounds are selected from the group consisting of hydrazine, primary diamines, secondary diamines, primary and secondary amino-containing compounds, and any mixtures thereof.

Preferably, the molar ratio between the active hydrogen present in the active hydrogen chain extending compound other than water and the isocyanate (NCO) groups present in the isocyanate-terminated polyurethane prepolymer is from 0.5:1 to 1.2:1, more preferably from 0.6:1 to 1.1:1, especially from 0.75:1 to 1.02:1, most preferably from 0.78:1 to 0.98: 1. Preferably, either the isocyanate-terminated polyurethane prepolymer is blended with an aqueous phase comprising a neutralizing agent and a chain extending compound, or the neutralized isocyanate-terminated polyurethane prepolymer is added to water comprising a chain extending compound, or (and more preferably) the neutralized isocyanate-terminated polyurethane is blended with an aqueous phase and the chain extending compound is added after blending.

The invention further relates to an aqueous coating composition comprising a polyurethane a and less than 3 wt.% of 1-methyl-2-pyrrolidone, wherein the polyurethane a comprises as structural units at least the following:

(a) a polyisocyanate containing at least two cyclic groups,

(c) a component containing isocyanate-reactive groups, wherein,

Wherein the weight ratio between (a) and (b) is from 50:50 to 99: 1;

wherein polyurethane a is prepared by: preparing a neutralized isocyanate terminated polyurethane prepolymer, dispersing the prepolymer in water, followed by chain extending the dispersed prepolymer with a chain extending compound selected from the group consisting of non-terminated hydrazine, non-terminated primary diamines, non-terminated secondary diamines, compounds containing non-terminated primary amino groups and non-terminated secondary amino groups, and any mixtures thereof. Non-limiting examples of compounds containing unblocked primary and unblocked secondary amino groups are 2- (methylamino) ethylamine, aminoethylethanolamine, aminoethylpiperazine, diethylenetriamine. The aqueous coating composition preferably comprises less than 1 wt% 1-methyl-2-pyrrolidone based on the solids content of the coating composition, more preferably the aqueous coating composition is free of 1-methyl-2-pyrrolidone. More preferably, the aqueous coating composition is solvent-free. It has surprisingly been found that polyurethane prepolymers obtained by reacting at least (a), (b) and (c) have a reduced viscosity compared to polyurethane prepolymers obtained by reacting at least (a) and (c), but not (b), thereby allowing the use of reduced amounts of solvent to prepare the prepolymers (resulting in the aqueous coating compositions of the present invention having a reduced VOC content) even allowing the preparation of polyurethane prepolymers without the use of solvents (resulting in zero VOC coating compositions).

The present invention also relates to a method of coating a substrate selected from the group consisting of wood, metal, plastic, linoleum, concrete, glass, and any combination thereof; wherein the method comprises:

(i) applying an aqueous coating composition as described above or obtained by the above method to a substrate; and

(ii) the aqueous coating composition is physically dried (by evaporation of volatiles) and optionally cured to obtain a coating.

The invention further relates to a substrate having a coating obtained by (i) applying the aqueous coating composition according to the invention or obtained by the process according to the invention to a substrate and (ii) physically drying (by evaporation of volatiles) and optionally curing the aqueous coating composition to obtain a coating. The substrate is preferably selected from the group consisting of wood, metal, plastic, linoleum, concrete, glass, packaging film, and any combination thereof. More preferably, a wood substrate is coated.

The invention will now be illustrated with reference to the following examples. All parts, percentages and ratios are by weight unless otherwise indicated.

As used herein, the singular forms of terms shall be construed to include the plural forms and vice versa, unless otherwise specified.

Components and abbreviations used

H12MDI ═ dicyclohexylmethane-4, 4' -diisocyanate from Covestro

IPDI ═ isophorone diisocyanate from Covestro

Mixture of 2,2, 4-trimethyl-hexamethylene diisocyanate and 2,4, 4-trimethyl-hexamethylene diisocyanate from Evonik, CAS number 32052-51-0

HDI-hexamethylene diisocyanate from Covestro

DMPA ═ dimethylolpropionic acid from Perstorp polyols

Durez-ter S1015-62-hexanediol neopentyl glycol adipate copolymer available from Durez, OHV 62mgKOH/g

pTHF 1000 polytetramethylene ether glycol with OH-number 112.5mg KOH/g from BASF

PC C2200 Desmophen C2200 from Covestro

CHDM-cyclohexanedimethanol available from Eastman Chemical

BMA ═ n-butyl methacrylate from Dow Chemical

MMA ═ methyl methacrylate from Dow Chemical

BHT ═ butylated hydroxytoluene (inhibitor) from Melisol

TEA-Triethylamine available from Arkema

Hydrazine-hydrazine solution in water [ 16% ], available from Arkema

IAA ═ isoascorbic acid available from Brenntag Volkers Benelux BV

tBHPO ═ tert-butyl hydroperoxide available from Akzo Nobel Chemicals BV

FeEDTA-Fe-EDTA complex, 1% in water

Dowanol DPM ═ di (propylene glycol) monomethyl ether (DDPM) from Dow Benelux

BYK346 ═ Silicone surfactant for waterborne coatings to improve substrate wetting, available from BYK

Examples

The following examples were prepared, coatings obtained and tested. The compositions of the examples and the results are shown in the following table.

Minimum film formation temperature MFFT

The MFFT is the lowest temperature at which the solid portion of the polymer or aqueous polymer dispersion (also known as latex or emulsion), which in turn serves as a binder for the remaining solids in the paint film, self-coalesces under semi-dry conditions to form a continuous polymer film. At a temperature of the MFFT of the polymer or above, a continuous film is formed. At temperatures below its MFFT, the polymer cannot coalesce to form a continuous film and therefore cannot bond to itself (or any pigments and extenders that may be present) and result in a "fractured, cracked or powdery" layer. MFFT was measured on the Rhopoint MFFT-90 minimum film formation temperature instrument using a wet film thickness of 90 μm.

Viscosity:measured with a Brookfield DV-I viscometer (spindle S61, 60rpm, 23 ℃).

Particle size

Particle size was determined by photon correlation spectroscopy using a Malvern Zetasizer Nano zs. The sample was diluted to a concentration of about 0.1g disp/liter.

Solids content

The solids content of the dispersions was determined on a Mettler Toledo HB43-S compact halogen moisture meter. At the start of the measurement, the moisture meter determines the weight of the sample, which is then heated to 130 ℃ by the integral halogen heating module and the volatile compounds evaporate. During the drying process, the instrument continuously measures the weight of the sample. After the drying is complete, the solids content of the sample will show up as the final result.

Preparation of polyurethane-vinyl Polymer hybrid Dispersion

Example 1

Stage 1: to a 1000cm cell equipped with a thermometer and an overhead stirrer³The flask was charged with HDI (36.7g), H12MDI (57.4g), DMPA (15.2g), Durez-ter S1015-62 (236.7g), BHT (0.5g) and MMA (104.0 g). The mixture was heated to 85 ℃ and held at 85 ℃ for 2 hours. The NCO content of the resultant isocyanate-terminated prepolymer was 2.9% (theoretical 3.6%). The mixture was then cooled to 80 ℃ and TEA (10.3g) was added. The NCO/OH molar ratio was 1.79.

A dispersion of isocyanate-terminated prepolymer was prepared by adding 307g of the isocyanate-terminated prepolymer mixture to deionized water (526g) over 1 hour. The temperature of the isocyanate-terminated prepolymer during the dispersion was maintained at 80 ℃ and the dispersion temperature was controlled between 25 and 30 ℃. After dispersion, 15.9% hydrazine (18.6g) was added to the dispersion.

Stage 2: the free-radical polymerization for preparing the polyurethane vinyl hybrid dispersion with a urethane/vinyl ratio of 77/23 was carried out as follows:

to the dispersion prepared in stage 1 were added 70% aqueous tert-butyl hydroperoxide (0.26g) and 1% aqueous FeEDTA (0.21g), followed by 1% aqueous erythorbic acid (14.0g) over 15 minutes.

The resulting polyurethane vinyl hybrid dispersion was filtered through a 75 micron filter cloth with the specifications given in table 2 below.

Examples 2-5 and comparative examples A-D

In examples 2-5 and comparative examples A-D, the process described in example 1 was repeated, except that different amounts and different compositions were used. These amounts and components are illustrated in table 1 below. In examples 2 and 3, the second acrylic phase was introduced by adding additional monomer. Unless otherwise indicated, the amounts of the various components are expressed in grams. The specifications of the resulting composition are shown in Table 2, and the film properties are shown in Table 4.

TABLE 1

Comparative example E

Comparative example E shows that the one-step prepolymer method does not result in a low viscosity polyurethane dispersion when NMP is used.

To a 2000cm cell equipped with a thermometer and an overhead stirrer³The flask was charged with components DMPA (50.8g), Durez-ter S1015-62(788.9g), NMP (346.5), HDI (122.41) and H12-MDI (191.5 g). The reaction was heated to 95 ℃ and held at this temperature for 2 hours. The NCO-content of the resultant isocyanate-terminated prepolymer was 3.4% (theoretically 3.6%) of the solid content. The prepolymer was cooled to 80 ℃ and TEA (37.9g) was added.

A dispersion of the isocyanate terminated prepolymer was prepared by adding 410g of the isocyanate terminated prepolymer to deionized water (341.0g) over 1 hour. During the dispersion, the temperature of the isocyanate-terminated prepolymer was maintained at 80 ℃ and the dispersion temperature was controlled at 25-30 ℃. During dispersion, the viscosity rapidly increased, forming a white high viscosity paste. The reaction was stopped.

Comparative example F

Comparative example F shows that without NMP a sequential process to first prepare the adduct of monomeric H12MDI with DMPA is not possible.

To a 1000cm cell equipped with a thermometer and overhead stirrer³The flask was charged with the component DMPA (15.2g), MMA (104.0g), Ionol cp (0.4g) and H12-MDI (57.4 g). The reaction was heated to 85 ℃ and held at this temperature for 2 hours. The reaction product was insoluble in MMA, resulting in phase separation and sedimentation, and the reaction was stopped.

TABLE 2

Brookfield viscosity (mPa.s) at 25 ℃

To 30g of the final dispersion of example 1 and comparative example A were added different amounts of the coalescing agent Dowanol DPM, 0.3[ 1% ], 0.6[ 2% ], 0.9[ 3% ] and 1.2g [ 4% ], respectively. As shown in table 3, the urethane/acrylic hybrid binder according to the present invention shows a low minimum film forming temperature and the need for coalescents is low.

TABLE 3

The dispersions prepared in examples 1-5 and comparative examples a-D were formulated as described in table 4. The formulated composition was cast onto Leneta test paper using a wire rod at a wet film thickness of 150 microns. The coalescent agent is added to the dispersion so that a continuous defect-free film can be formed under the applied temperature conditions, so that the stain resistance of the coating can be determined. The cast film was then dried at room temperature for 24 hours and then aged at 50 ℃ for 16 hours. The coating was allowed to cool to room temperature for 1 hour. The coated cards were then evaluated for stain resistance to the following stains: ammonia, water, red wine, ethanol (48%), coffee. In all cases, spots (1 cm) of the respective stains were identified²) Placed on the coating and covered with a piece of filter paper and a piece of crystal. After the test period, the spots were wiped off gently with tissue paper and the integrity of the film was assessed. A score between 0 and 5, wherein:

grade 5-no change; the test area is indistinguishable from the adjacent surrounding area.

4-minor variations; only when the light source images on the test surface and reflects towards the eyes of the observer, the test area is distinguishable from the adjacent surrounding areas, e.g. discoloration, gloss and color change. There were no surface structural changes such as swelling, fiber wrinkling, cracking, blistering.

Grade 3-moderate change; the test area is distinguishable from the adjacent surrounding areas and is visible in several viewing directions, e.g. discoloration, gloss and color change. There were no surface structural changes such as swelling, fiber wrinkling, cracking, blistering.

Grade 2-major change; the test area is clearly different from the adjacent surrounding area and is visible in several viewing directions, e.g. discoloration, gloss and color change.

Grade 1-large variation; the test area is distinct from the adjacent surrounding area and is visible in several viewing directions, e.g., discoloration, gloss and color change, and/or the surface material is completely or partially removed.

For comparative example a, 7 wt% Dowanol DPM was required to obtain a continuous film starting from a WFT of 150 μm.

The stain resistance of the example coatings versus the comparative example coatings clearly shows that with low amounts of coalescent, a sufficient level and similar levels of stain resistance for the majority can be achieved. Reducing the amount of Dowanol DPM of comparative examples a-D resulted in failure to obtain a continuous defect free film and therefore the stain resistance of the coating was very poor.

TABLE 4

The results shown in tables 2 and 4 show that the additional use of HDI leads to a reduction in MFFT (i.e. <5 ℃ vs29 ℃, example 1vs comparative a and 40 ℃ vs55 ℃, example 5vs comparative B, see table 2), while the tolerance to ammonia, red wine and water remains at the same level, the tolerance to ethanol remains at the same level or even improves, and the tolerance to coffee deteriorates only to a limited extent, even with lower amounts of coalescing agent (Dowanol DPM). Further, comparison of comparative example C with comparative example D additionally shows that the additional use of HDI leads to a higher reduction in MFFT in the case of using H12MDI than IPDI (see Table 2: reduction in MFFT due to the use of HDI of 7 ℃ in the case of using IPDI; reduction in MFFT due to the use of HDI of at least 15 ℃ in the case of using H12MDI (example 5: reduction in MFFT of 15 ℃ compared with comparative example B; example 1: reduction in MFFT of more than 24 ℃ compared with comparative example A), whereas the stain resistance is not significantly affected by the use of HDI for IPDI and H12 MDI).

Claims

1. An aqueous coating composition comprising a polyurethane a and a vinyl polymer, wherein the polyurethane a comprises as structural units at least the following:

(a) a polyisocyanate containing at least two cyclic groups,

(b) a non-cyclic aliphatic diisocyanate in which the non-cyclic aliphatic group linking the two isocyanate groups has 4 to 9 carbon atoms, and

(c) a component containing isocyanate-reactive groups, wherein,

wherein the total amount of (a) and (b) is 10-60% by weight relative to the total weight of the components used to prepare the polyurethane A; and is provided with

Wherein the weight ratio between (a) and (b) is in the range of 50:50 to 99: 1; and is provided with

Wherein the amount of 1-methyl-2-pyrrolidone in the aqueous coating composition is less than 3 weight percent of the solids content of the coating composition, and wherein the coating composition contains tin in an amount of up to 2 ppm.

2. An aqueous coating composition according to claim 1, wherein the weight ratio of (a) to (b) is from 60:40 to 95: 5.

3. An aqueous coating composition according to any one of the preceding claims, wherein component (a) is selected from polyisocyanates containing at least two cycloaliphatic groups, polyisocyanates containing at least two aromatic groups and any mixtures thereof.

4. An aqueous coating composition according to claim 1 or 2, wherein component (a) is a polyisocyanate containing at least two cycloaliphatic groups.

5. An aqueous coating composition according to claim 1 or 2, wherein component (a) is H₁₂MDI, CAS number 5124-30-1.

6. An aqueous coating composition according to claim 3, wherein the polyisocyanate containing at least two aromatic groups is a mixture of 4,4 '-methylene bis (phenyl isocyanate) and 2,4' -methylene bis (phenyl isocyanate).

7. An aqueous coating composition according to claim 1 or 2, wherein component (b) is a non-cyclic aliphatic C4-C9 diisocyanate.

8. An aqueous coating composition according to claim 1 or 2, wherein component (b) is 1, 6-diisocyanatohexane, CAS number 822-06-0.

9. An aqueous coating composition according to claim 1 or 2, wherein the polyurethane a is prepared by preparing a neutralized isocyanate-terminated polyurethane prepolymer which is dispersed in water and subsequently chain extending the dispersed prepolymer with a chain extending compound selected from the group consisting of hydrazine, primary diamines, secondary diamines, primary and secondary amino group containing compounds, and any mixtures thereof.

10. An aqueous coating composition according to claim 1 or 2, wherein the acid number of the polyurethane a is from 5 to 65mg KOH/g polyurethane a.

11. An aqueous coating composition according to claim 1 or 2, wherein the coating composition has a minimum film forming temperature of less than 50 ℃ and contains less than 10% by weight of coalescent agents.

12. An aqueous coating composition according to claim 1 or 2, wherein the weight ratio of polyurethane to vinyl polymer present in the coating composition is from 95:5 to 15: 85.

13. An aqueous coating composition according to claim 1 or 2, wherein the vinyl polymer is prepared by free radical polymerization of vinyl monomers in the presence of the polyurethane a, the coating composition comprising a polyurethane vinyl polymer hybrid dispersion.

14. An aqueous coating composition according to claim 1 or 2, wherein the amount of 1-methyl-2-pyrrolidone in the aqueous coating composition is less than 1% by weight of the solids content of the coating composition.

15. An aqueous coating composition according to claim 1 or 2, wherein the coating composition contains a tertiary amine in an amount of up to 1.5 wt.%.

16. An aqueous coating composition according to claim 1 or 2, wherein the total amount of polyurethane a and vinyl polymer present in the aqueous coating composition is from 20 to 55 wt.%, relative to the weight of the aqueous coating composition.

17. An aqueous coating composition according to claim 1, wherein the weight ratio of (a) to (b) is from 65:35 to 90: 10.

18. An aqueous coating composition according to claim 1 or 2, wherein component (b) is a non-cyclic aliphatic C4-C8 diisocyanate.

19. An aqueous coating composition according to claim 1 or 2, wherein the weight ratio of polyurethane to vinyl polymer present in the coating composition is from 90:10 to 20: 80.

20. An aqueous coating composition according to claim 1 or 2, wherein the amount of 1-methyl-2-pyrrolidone in the aqueous coating composition is less than 0.5 wt% of the solids content of the coating composition.

21. An aqueous coating composition according to claim 1 or 2, wherein the amount of 1-methyl-2-pyrrolidone in the aqueous coating composition is 0 wt%.

22. A process for preparing an aqueous coating composition according to any one of the preceding claims, comprising the steps of:

(a) a polyisocyanate containing at least two cyclic groups,

(d) adding 0-40 wt% of diluent in the step I,

wherein the total amount of (a) and (b) is 10-60% by weight relative to the total weight of the components used to prepare polyurethane A;

(a) and (b) in a weight ratio of 50:50 to 99: 1; and is provided with

(d) The amounts of (a), (b), (c) and (d);

either mixing the isocyanate-terminated polyurethane prepolymer with an aqueous phase comprising a neutralizing agent and optionally further chain extending compounds or neutralizing the isocyanate-terminated polyurethane prepolymer by adding a neutralizing agent to the isocyanate-terminated polyurethane prepolymer and subsequently (i) adding the neutralized isocyanate-terminated polyurethane prepolymer to water optionally comprising further chain extending compounds or (ii) adding water optionally comprising further chain extending compounds to the neutralized isocyanate-terminated polyurethane prepolymer; and

wherein the process comprises feeding at least one of components (c) (i), (c) (ii) and (c) (iii) and components (a) and (b) to a reactor at the beginning of the reaction to produce the isocyanate-terminated polyurethane prepolymer; and

wherein the preparation of the polyurethane a is carried out in the presence of less than 3 wt% of 1-methyl-2-pyrrolidone, based on the weight of the polyurethane a; and

wherein (i) the vinyl polymer is introduced into the coating composition before, during or after the preparation of the polyurethane and/or (ii) a vinyl monomer is added before, during or after the preparation of the polyurethane and the vinyl monomer is polymerized in the presence of the polyurethane.

23. The process according to claim 22, wherein the chain extension of the isocyanate-terminated polyurethane prepolymer is carried out with hydrazine, a primary diamine, a secondary diamine, a compound containing primary and secondary amino groups, and any mixture thereof.

24. An aqueous coating composition comprising polyurethane a and less than 1 wt% of 1-methyl-2-pyrrolidone, based on the weight of the solids content of the coating composition, and comprising tin in an amount of up to 2ppm, wherein the polyurethane a comprises at least the following as structural units:

(a) a polyisocyanate containing at least two cyclic groups,

(c) a component containing isocyanate-reactive groups, wherein,

wherein the total amount of (a) and (b) is 10-60% by weight relative to the total weight of the components used to prepare the polyurethane A; and is

Wherein the weight ratio between (a) and (b) is from 50:50 to 99: 1;

wherein the polyurethane a is prepared by preparing a neutralized isocyanate-terminated polyurethane prepolymer dispersed in water and subsequently chain extending the dispersed prepolymer with a chain extending compound selected from the group consisting of an unblocked hydrazine, an unblocked primary diamine, an unblocked secondary diamine, a compound containing an unblocked primary amino group and an unblocked secondary amino group, and any mixtures thereof.

25. A substrate having a coating obtained by: (i) applying an aqueous coating composition according to any one of claims 1 to 21 or 24 or obtained by the method of claim 22 or 23 on a substrate, and (ii) physically drying and optionally curing the aqueous coating composition.

26. The substrate of claim 25, wherein the substrate is selected from the group consisting of wood, metal, plastic, linoleum, concrete, glass, and any combination thereof.

27. The substrate of claim 25, wherein the substrate is wood.

28. A method of coating a substrate selected from the group consisting of wood, metal, plastic, linoleum, concrete, glass, and any combination thereof; wherein the method comprises:

(i) applying an aqueous coating composition according to any one of claims 1 to 21 or 24 or obtained by the method of claim 22 or 23 to a substrate; and

(ii) physically drying and optionally curing the aqueous coating composition to obtain a coating.